ICES Journal of
Marine Science
ICES Journal of Marine Science (2016), 73(3), 927– 936. doi:10.1093/icesjms/fsv226
Contribution to Special Issue: ‘Towards a Broader Perspective on Ocean Acidification Research’
Original Article
Ocean acidification does not alter grazing in the calanoid copepods
Calanus finmarchicus and Calanus glacialis
Nicole Hildebrandt1 *, Franz J. Sartoris 1, Kai G. Schulz 2,3, Ulf Riebesell 2, and Barbara Niehoff1
1
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, Bremerhaven 27570, Germany
GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, Kiel 24105, Germany
3
Centre for Coastal Biogeochemistry, School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore, NSW 2480,
Australia
2
*Corresponding author: tel: +49 471 4831 1810; fax: +49 471 4831 1149; e-mail: [email protected]
Hildebrandt, N., Sartoris, F. J., Schulz, K. G., Riebesell, U., and Niehoff, B. Ocean acidification does not alter grazing in the calanoid
copepods Calanus finmarchicus and Calanus glacialis. – ICES Journal of Marine Science, 73: 927 – 936.
Received 30 June 2015; revised 4 November 2015; accepted 5 November 2015; advance access publication 13 December 2015.
It is currently under debate whether organisms that regulate their acid–base status under environmental hypercapnia demand additional energy.
This could impair animal fitness, but might be compensated for via increased ingestion rates when food is available. No data are yet available for
dominant Calanus spp. from boreal and Arctic waters. To fill this gap, we incubated Calanus glacialis at 390, 1120, and 3000 matm for 16 d with
Thalassiosira weissflogii (diatom) as food source on-board RV Polarstern in Fram Strait in 2012. Every 4 d copepods were subsampled from all
CO2 treatments and clearance and ingestion rates were determined. During the SOPRAN mesocosm experiment in Bergen, Norway, 2011, we
weekly collected Calanus finmarchicus from mesocosms initially adjusted to 390 and 3000 matm CO2 and measured grazing at low and high
pCO2. In addition, copepods were deep frozen for body mass analyses. Elevated pCO2 did not directly affect grazing activities and body mass, suggesting that the copepods did not have additional energy demands for coping with acidification, neither during long-term exposure nor after immediate changes in pCO2. Shifts in seawater pH thus do not seem to challenge these copepod species.
Keywords: Calanus, clearance rate, CO2, food uptake, ingestion rate.
Introduction
Anthropogenic CO2 emissions, which recently amounted to 34
billion tons year21 (Friedlingstein et al., 2010), have increased the
atmospheric CO2 concentration since pre-industrial times from
280 to 400 matm (Tans, 2014). About 30% of the emitted CO2
is absorbed by the world’s oceans (Solomon et al., 2007), making
them the second largest sink for human-made CO2. The CO2
uptake changes seawater chemistry, resulting in decreasing seawater
pH and carbonate ion concentrations (Raven et al., 2005). Model
calculations based on the IPCC emissions scenario IS92a (Alcamo
et al., 1995) projected that CO2 concentrations might increase to
750 matm by 2100 and to almost 2000 matm by the year 2300
(Caldeira and Wickett, 2003), with a corresponding decline in
surface ocean pH by 0.4 units until the end of the century and
by a maximum of 0.77 units until 2300, a process usually referred
to as “ocean acidification” (OA).
# International
OA has the potential to severely affect the performance of marine
organisms. Metabolic rates can be depressed at elevated CO2 concentrations (Reipschläger and Pörtner, 1996; Rosa and Seibel,
2008; Seibel et al., 2012), possibly triggered by a lack of or incomplete
compensation for increasing pCO2 in extracellular fluids due to environmental hypercapnia (Reipschläger and Pörtner, 1996; Pörtner
et al., 1998). Food uptake and growth may then be impaired and
mortality may increase (Michaelidis et al., 2005; Miles et al., 2007;
Appelhans et al., 2012; Vargas et al., 2013). For species that are
able to actively regulate their internal acid–base balance, such as
crustaceans (Widdicombe and Spicer, 2008), it is discussed that
additional energy has to be allocated to maintaining the acid–
base status, and therefore fitness is lowered at elevated seawater
pCO2 (Wood et al., 2008; Thomsen and Melzner, 2010; Melzner
et al., 2011; Appelhans et al., 2012, Saba et al., 2012). Therefore,
negative effects seem to be particularly distinct when food is
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928
limited (Melzner et al., 2011; Appelhans et al., 2012), while, when
food supply is sufficient, feeding rates may increase to meet the additional energy demands, as suggested for krill (Saba et al., 2012) and
the calanoid copepod Centropages tenuiremis (Li and Gao, 2012).
Calanoid copepods are key players in pelagic marine environments and often dominate zooplankton communities (Longhurst,
1985). Studies on the sensitivity of copepods to future OA show
mixed responses. Levels of OA that are predicted to occur until
2300 were detrimental in four species. Dupont and Thorndyke
(2008) reported that generation times in Acartia tonsa increased
under elevated pCO2. Cripps et al. (2014) showed for the same
species that hatching success and nauplii survival are also sensitive
to OA. In A. spinicauda and C. tenuiremis, survival of females as
well as egg hatching rates was negatively affected (Zhang et al.,
2011), and in Pseudocalanus acuspes, egg production rates significantly decreased (Thor and Dupont, 2015). In all other species
studied so far, parameters such as growth, egg production, hatching
success and survival of nauplii, copepodites and adults were only
affected at CO2 concentrations ≥5000 matm, if at all (e.g. Kurihara
et al., 2004; Zhang et al., 2011; Mayor et al., 2012; McConville et al.,
2013; Pedersen et al., 2013; Isari et al., 2015). Under controlled laboratory conditions, food uptake of calanoid copepods in response
to elevated pCO2 has only been studied in two species so far. In C.
tenuiremis, grazing rates decreased at elevated pCO2 (1000 matm)
during the 1 d of exposure; however, no significant effects were
found thereafter (Li and Gao, 2012). In P. acuspes, effects of OA
(800 and 1400 matm CO2) on ingestion rates were non-linear,
and also dependent on the geographical region and food concentration (Thor and Oliva, 2015).
In our study, we focus on two Calanus species, i.e. C. finmarchicus
(Gunnerus, 1770) and Calanus glacialis Jaschnov (1955). Both are
important components of the lipid-based foodweb of the Arctic
(Falk-Petersen et al., 2007 and references therein). Calanus finmarchicus is a North Atlantic species and is transported into the
Arctic Ocean via the West Spitsbergen Current, into the Barents
Sea with the North Cape Current and into Davis Strait with the
West Greenland Current (e.g. Jaschnov, 1970; Conover, 1988).
Calanus glacialis has its origin in the Arctic shelf regions and penetrates southward into Fram Strait with the East Greenland Current
(Jaschnov, 1970; Conover, 1988). In areas where the warm Atlantic
water submerges under the cold Arctic water, both species co-occur
(Conover, 1988). During spring and summer, they inhabit surface
waters where they feed on phytoplankton and accumulate large
lipid stores (e.g. Marshall and Orr, 1955; Lee, 1974; Pasternak
et al., 2001). In late summer, they descend to deeper waters and
enter a diapause to sustain the food scarce period in winter (e.g.
Tande et al., 1985; Hirche, 1998). The natural seawater pH the copepods experience during their seasonal migrations ranges from 8.2
in surface waters (Charalampopoulou et al., 2008) to 7.9 in deep
waters (Jutterström et al., 2010).
Previous studies on the effects of OA on mortality, body mass,
metabolic rates, and reproductive output of C. finmarchicus and
C. glacialis indicate that copepodites V (CV) and females are
robust to CO2 levels predicted for the next centuries (Mayor et al.,
2007; Weydmann et al., 2012; Hildebrandt et al., 2014). Feeding
has not been studied under controlled laboratory conditions yet;
however, Pedersen et al. (2013) published a study on C. finmarchicus
that were raised from eggs to adults at CO2 concentrations of 3300–
9700 matm and showed that fat contents in CV grown at control and
elevated pCO2 were similar. We may thus hypothesize that the food
uptake was not lowered by high CO2 concentrations. It remains
N. Hildebrandt et al.
open, however, whether C. finmarchicus compensated for additional
energy demands due to OA stress with an increase in grazing rates
(Saba et al., 2012). At more realistic surface seawater CO2 concentrations (≤1420 matm), de Kluijver et al. (2013) examined trophic
interactions during a 30-day mesocosm study in an Arctic fjord,
using 13C as a tracer. Their study found reduced rates of 13C incorporation in Calanus spp. in high pCO2 mesocosms, indicating that
grazing rates decrease with increasing pCO2. However, as the food
quality, i.e. the algal community composition in the mesocosms,
changed with the CO2 concentration (Brussaard et al., 2013;
Schulz et al., 2013), the decrease in grazing could reflect indirect
effects of OA.
To elucidate whether Calanus spp. ingest more food to compensate
for additional energy demands or whether ingestion rates decrease
when exposed to OA, we performed controlled laboratory experiments at different pCO2, feeding the copepods with monoalgal food
(Thalassiosira weissflogii). Part of our study was conducted within
the SOPRAN 2011 mesocosm experiment in Bergen, Norway. Here,
we weekly sampled C. finmarchicus from mesocosms initially adjusted
to 390 and 3000 matm CO2 and exposed the copepods of each group to
both, high and low pCO2 conditions to study immediate responses to
changing pCO2 as well as long-term effects of exposure to high pCO2.
In addition, we incubated C. glacialis at 390, 1120, and 3000 matm CO2
for 16 d in the cold-rooms on-board RV Polarstern and repeatedly
conducted grazing experiments.
Methods
Experiments during the SOPRAN mesocosm study 2011
Sampling
In May and June 2011, experiments were conducted within the
framework of the SOPRAN mesocosm experiment at Espegrend,
the Marine Biological Station of the University of Bergen, Norway.
Nine KOSMOS (Kiel Offshore Mesocosms for Future Ocean
Simulations) mesocosms of 25 m length and 2 m diameter were
deployed in the Raunefjord at N 608 15.87′ , E 0058 12.33′ for 6
weeks. For technical details on the mesocosms and their deployment, see Riebesell et al. (2013). Briefly, each mesocosm enclosed
75 m3 of fjord water containing natural plankton ,3 mm.
Larger mesozooplanktonic and nektonic organisms were excluded
by a mesh (3 mm mesh size) that covered the openings of the mesocosm bags during deployment, as these organisms occur only in low
numbers and are patchily distributed. On the lower end of each
mesocosm, a sediment trap was installed to collect settling material.
Ambient fjord water was aerated with pure CO2 and added to seven
of the mesocosms in five steps over 5 d to adjust the pH to 390,
560, 840, 1120, 1400, 2000, and 3000 matm CO2, while
two mesocosms were kept at in situ pCO2 (280 matm). For our
experiments, only copepods from the mesocosms with 390 (control)
and 3000 matm CO2 (high pCO2) were used. The pH (reported on
the total scale) in the control mesocosm ranged between 8.0 and
8.1 throughout the experiment. In the high CO2 mesocosm, the
initial pH after CO2 manipulation was 7.2. However, due to outgassing and biological activities, it increased over time, especially in
the upper water column. At the end of the experiment, the pH was
7.8 at the surface and 7.4 at depth. On Day 14, nutrients
(5 mmol l21 NO3, 0.16 mmol l21 PO4) were added to the mesocosms to induce a phytoplankton bloom.
Once a week zooplankton was sampled with an Apstein net
(mesh size 55 mm). Sampling was performed in the fjord on Day
0 and thereafter in the nine mesocosms. Sampling depth was
929
Ocean acidification does not alter grazing in Calanus spp.
limited to 23 m in order not to resuspend material from the sediment traps. Within 1 h, the plankton samples were brought to a
cold room adjusted to 108C, which was the approximate in situ temperature at that time.
Preparation of experimental water and food algae
Filtered seawater was adjusted to target values of 390 (control) and
3000 matm CO2 (high CO2) by mixing with filtered CO2 saturated
fjord water. The pH was monitored with a pH electrode (Mettler
Toledo InLab Routine Pt1000, connected to a pH meter WTW
pH 3310), which was calibrated with NIST buffers (pH 6.865 and
9.180). Then the pH was converted to total scale (pHT) using
TRIS-based reference material (Batch no. 4, A. Dickson, Scripps
Institution of Oceanography). Dissolved inorganic carbon (DIC)
in the experimental water was measured with a Technicon
Analyzer TrAAcs 800 (Seal Analytical GmbH, Germany). pHT and
DIC were then used to calculate DIC using the programme
CO2SYS (Lewis and Wallace, 1998). Mean pH values of control
and high CO2 treatments were 7.9 (592 + 42 matm pCO2) and 7.2
(3202 + 521 matm pCO2), respectively (Table 1). Temperature
and salinity were determined with a conductivity meter WTW
Cond340i (Table 1). Monocultures of the diatom T. weissflogii
were grown in f/2 medium (Guillard, 1975) at 10 8C under constant
light as food for the copepods.
Determination of grazing rates
About 60 C. finmarchicus copepodites V (CV) were sorted from the
control and high CO2 mesocosm sample, respectively. To eliminate
the effect of possibly different feeding conditions in the mesocosms
on grazing rates during the experiments, the copepods were preincubated for 1 d at 108C in filtered seawater adjusted to the respective CO2 concentration and containing T. weissflogii in excess.
For the determination of grazing rates, high and control
CO2 water was inoculated with T. weissflogii at a concentration of
4000 cells ml21. Thirty copepods each from pre-incubation at
control and pre-incubation at high pCO2 were transferred to 1 l
bottles (10 copepods bottle21) containing seawater of the respective
pCO2. To test whether immediate changes in CO2 concentration
affect the food uptake, 30 copepods from pre-incubation at control
seawater pH were placed in three 1 l bottles containing high CO2
water, and 30 copepods from the pre-incubation at high pCO2
were transferred to 1 l bottles with control seawater. Three additional bottles for each CO2 concentration were prepared that contained
seawater with algae but no copepods. These bottles were run as a
blank to correct the grazing rates of the copepods for algal growth.
After transfer of algal suspensions and copepods, all bottles were
immediately sealed airtight and mounted to a plankton wheel for
17.5 to 22 h in the dark. After the experiment, the copepods were
sorted from all bottles, rinsed in distilled water and stored in
groups of two to six in tin caps at 2208C to measure C and N
content. Subsamples of 3 × 100 ml of the experimental water for
each CO2 treatment were filtered on GF/F filters and frozen to determine the chlorophyll a (chl a) concentration before and at the
end of the experiments.
Prosome length of C. finmarchicus was measured under a stereomicroscope with an ocular micrometre (error + 5 mm) in 36 individuals sampled from the fjord at the beginning of the study.
On-board incubation experiment
Copepod sampling and incubation
The experiment with C. glacialis was conducted in July 2012 during
a cruise with RV Polarstern to Fram Strait (ARK-XXVII/1 and 2).
Copepods were sampled with vertical bongo net hauls (200 and
300 mm mesh size, 0 –250 m) at approximately N 798 40.3′ , W
0118 59.3′ (PS 80/91) and immediately brought to a cooling container adjusted to 08C. About 1350 C. glacialis CV were sorted
from the samples and acclimated to laboratory conditions in filtered
seawater enriched with T. weissflogii for 2 d.
Preparation of incubation water and food algae
Filtered seawater was adjusted to 1120 (intermediate) and 3000 matm
(high) CO2 by bubbling with gas mixtures from a gas cylinder
(purchased from Air Liquide Deutschland GmbH, Düsseldorf).
Untreated filtered seawater was used as a control (390 matm). The
resulting pH values (Table 1) differed at least by 0.3 units between
control and intermediate and between intermediate and high CO2
treatments. There was no possibility to measure DIC samples onboard, and as storage of such samples for a period of several months,
until the return of RV Polarstern to Bremerhaven, is not recommended, we did not measure parameters other than pH. However,
preliminary tests have shown that bubbling with the used air/CO2
mixes yield the desired seawater pCO2. T. weissflogii was cultured
according to the experiment in 2011, but at temperatures of 10 and
188C. Before it was fed to the copepods, the algal suspension was
adjusted to the incubation temperature.
CO2 incubation
The copepods were transferred to 6 l glass bottles and incubated at
control, intermediate and high CO2 for 16 d. Three bottles, each
containing 150 C. glacialis, were set up for each CO2 treatment.
The copepods were fed daily with T. weissflogii at a concentration
of 8000 cells ml1 to prevent food limitation as these large bottles
could not be mounted on a plankton wheel and therefore part of
the algae sank to the bottom. Every 4 d, the incubation water was
completely changed and pH, salinity, and temperature were measured. pH values increased on average by 0.19, 0.13, and 0.06
Table 1. Water parameters during the determination of grazing rates (a) and during the CO2 incubations on RV Polarstern in 2012 (b).
(a)
(b)
Species
C. finmarchicus
C. finmarchicus
C. glacialis
C. glacialis
C. glacialis
C. glacialis
C. glacialis
C. glacialis
CO2 treatment (matm)
390
3000
390
1120
3000
390
1120
3000
Temp. (88 C)
10.0 + 0.3
9.9 + 0.2
1.1 + 0.7
1.0 + 0.7
1.0 + 0.7
1.4 + 0.3
1.3 + 0.4
1.3 + 0.4
Salinity (psu)
32.4 + 0.2
32.4 + 0.4
32.4 + 1.2
32.9 + 0.5
32.7 + 0.7
33.2 + 0.4
33.1 + 0.4
33.3 + 0.4
Values are presented as mean + SD. Temp., temperature; N, number of measurements throughout the experiments/incubations.
pH (total scale)
7.86 + 0.03
7.16 + 0.07
7.97 + 0.06
7.62 + 0.04
7.21 + 0.05
7.86 + 0.13
7.54 + 0.09
7.21 + 0.07
N
4
4
5
5
5
24
24
24
930
N. Hildebrandt et al.
units in between water exchanges at 390, 1120, and 3000 matm CO2,
respectively. When the water was changed, 10 copepods from each
bottle were removed to determine grazing rates. Thus, the number
of copepods in the bottles decreased over time. At start and at the
end of the CO2 incubation, 36 –66 copepods from each CO2 treatment were measured under a stereomicroscope with an ocular
micrometre (prosome length) then deep-frozen individually for C
and N measurements.
Determination of grazing rates
Thirty copepods from each of the three different CO2 treatments
were transferred to three 1 l bottles (10 copepods bottle21) with seawater of the respective pCO2. T. weissflogii was added at a concentration of 2000 cells ml21. Along with three blanks for each CO2
concentration (see above), the bottles were mounted to a plankton
wheel for 21.5– 25 h. Subsamples for chl a measurements as well as
copepod C and N samples were taken as described above.
HEKAtech GmbH, Wegberg, Germany). Acetanilide was used as a
standard.
Statistics
Statistical analyses were performed with SigmaStat 3.5 (Systat
Software, Inc.). A t-test or a one-way ANOVA followed by a post
hoc Holm-Sidak test was performed to identify differences in
grazing and body mass between copepods from different CO2 treatments at each experimental day. A Spearman rank-order correlation
was used to identify changes in body carbon and nitrogen during the
experiments, and to test for correlation between CR/IR and the
initial chl a content in the incubation water to determine whether
our food concentrations limited grazing rates. Data were considered
significantly different at a p , 0.05. Results are presented as
mean + standard deviation.
Results
Sample analysis
To determine the chl a concentration in the incubation bottles and
blank bottles at the start and the end of the grazing experiments, the
algal cells on the GF/F filters were first disrupted in 90% acetone
using ultrasound (Branson Sonifier 250, Heinemann, Schwäbisch
Gmünd, Germany). Then, the chl a was extracted from the algal
cells for 2 h in the dark at 58C. After centrifugation at 4500 rpm
for 15 min at 08C, the chl a fluorescence in the supernatant was
determined with a Turner fluorometer (TD-700, Turner Designs,
Sunnyvale, CA, USA) at 665 nm before and after adding two
drops of 1 N HCl. Clearance rates (CRs) and ingestion rates (IRs)
of the copepods were then calculated after Frost (1972).
On some days, initial chl a concentrations were significantly different among CO2 treatments (C. finmarchicus: Day 8; C. glacialis:
Days 1 and 8). In order not to bias the results of the grazing experiments, we excluded the grazing rates that were measured on these
days from our analyses.
To determine carbon and nitrogen content, the copepods in the
tin caps were dried at 608C for 48 h then combusted with subsequent
gas chromatographic separation by an elemental analyser (Euro EA,
Mean initial chl a concentrations ranged between 7.8 and 9.6 mg l21
in the grazing experiments with C. finmarchicus CV from Bergen and
between 3.9 and 6.2 mg l21 in the experiments on-board RV
Polarstern with C. glacialis CV (Table 2). The concentrations were
significantly different among days but not among the pCO2 treatments at a specific day. At the end of the grazing experiment, chl a
concentrations were still high at 5.6 –9.5 (C. finmarchicus) and
1.4 –4.3 mg l21 (C. glacialis).
In C. finmarchicus collected from the Raunefjord on Day 0 of
the mesocosm experiment, clearance and ingestion rates at control
pCO2 were 2.2 + 0.7 ml copepod21 h21 and 0.018 + 0.005 mg chl
a copepod21 h21, respectively (Figure 1). On Days 15, 22, and 28,
C. finmarchicus were collected from the control (390 matm) and
high pCO2 mesocosm (initially 3000 matm), and grazing rates
were determined at the respective CO2 concentrations. Mean CR
(Figure 1a) and IR (Figure 1b) were similar to the control values
measured at Day 0. The pCO2 generally did not affect the grazing
rates. Only during the experiment on Day 28, CR and IR were significantly lower in copepods from the control than from the high pCO2
mesocosm (Table 3). Neither CR nor IR correlated with the initial
Table 2. Chlorophyll a concentration (mean + SD, n ¼ 3) in the experimental water at the start and at the end of grazing experiments with
Calanus spp. as well as in blank bottles.
Chlorophyll a (mg l21)
Species
C. finmarchicus
C. glacialis
Day
0
15
15
22
22
28
28
4
4
4
12
12
12
16
16
16
CO2 treatment
390
390
3000
390
3000
390
3000
390
1120
3000
390
1120
3000
390
1120
3000
Start
9.6 + 0.3
7.9 + 0.1
7.8 + 0.1
9.0
8.7
9.3
9.4
3.9 + 0.3
4.1 + 0.2
3.9 + 0.2
4.7 + 0.2
5.1 + 0.3
4.7 + 0.2
6.0 + 0.2
6.2 + 0.5
5.4 + 0.6
On Days 22 and 28 (C. finmarchicus), there was only one start measurement for chlorophyll a.
End
9.5 + 0.9
5.6 + 0.6
6.0 + 0.4
5.8 + 0.7
6.6 + 1.1
9.5 + 0.4
9.0 + 1.5
1.4 + 0.3
1.7 + 0.3
1.6 + 0.4
3.1 + 0.4
3.7 + 0.5
4.0 + 0.6
3.7 + 0.7
4.3 + 0.1
3.1 + 0.5
Blank (end)
12.0 + 3.6
8.5 + 1.4
8.8 + 0.4
8.6 + 2.5
9.8 + 0.7
11.0 + 0.6
12.0 + 0.5
3.6 + 0.3
3.9 + 0.1
3.7 + 0.3
5.2 + 0.3
5.6 + 0.4
5.2 + 0.2
5.9 + 0.7
6.2 + 0.1
5.9 + 0.4
931
Ocean acidification does not alter grazing in Calanus spp.
Figure 1. Long-term response of C. finmarchicus CV to OA: clearance
rate (a) and ingestion rate (b) at control (white circles) and high pCO2
(black circles). Data on Day 0 present only control measurements at low
pCO2, conducted before the adjustment of the pH in the mesocosms.
Data are presented as mean + standard deviation. Asterisk marks
significant differences between CO2 treatments.
Table 3. Results of the one-way ANOVAs to test for differences in
grazing rates of C. finmarchicus and C. glacialis among different CO2
treatments.
Species
C. finmarchicus
Parameter
CR
IR
C. glacialis
CR
IR
Day
15
22
28
15
22
28
4
12
16
4
12
16
d.f.
3
3
3
3
3
3
2
2
2
2
2
2
F
1.985
1.064
10.701
2.342
1.254
12.954
0.212
2.244
3.626
2.134
2.435
2.586
p
0.205
0.417
0.004
0.160
0.353
0.002
0.815
0.187
0.093
0.200
0.168
0.155
Power
0.172
0.057
0.955
0.222
0.080
0.983
0.050
0.178
0.335
0.166
0.200
0.217
Values presented in bold indicate significant differences in grazing rates
among CO2 treatments. CR, clearance rates; IR, ingestion rates. In
C. finmarchicus, the analysis compares data from both long-term and
immediate response groups.
chl a content in the incubation water (p . 0.05), indicating that
food concentrations did not limit grazing.
Also sudden changes in pCO2 did not affect the grazing activity
(Figure 2, Table 3). In copepods transferred from control to high
Figure 2. Immediate response of C. finmarchicus CV to OA: clearance
rate (a) and ingestion rate (b) of copepods originating in the high CO2
mesocosm that were incubated at control pCO2 (white circles) and of
copepods originating in the control mesocosm that were incubated at
high pCO2 (black circles). The data on Day 0 present only control
measurements at low pCO2, conducted before the adjustment of the
pH in the mesocosms. Data are presented as mean + standard
deviation, except for Day 15, where only two data points were available
for the high pCO2 treatment. Here, both data points are shown
separately.
CO2 and vice versa, CR and IR at Days 15 and 22 were again
similar to the rate measured on Day 0, whereas lower rates (CR:
0.9 ml copepod21 h21, IR: 0.009 mg chl a copepod21 h21) were
measured on Day 28. Again, no correlation was found between
CR or IR and the initial chl a content (p . 0.05).
The mean C and N contents of C. finmarchicus CV (2.4 + 0.1 mm
prosome length) from the control mesocosms were 161 and 19 mg, respectively (Table 4), and did not change significantly over time
(Table 5). In copepods from the high CO2 mesocosm, the C and N
contents were significantly lower when compared with copepods
from the control mesocosm on Days 8 and 15 (t-test, 0.001 ≤ p ≤
0.008). On the last two sampling days, however, C and N had
increased, and no differences in body mass were found between copepods from high and control mesocosms (Tables 4 and 5).
In C. glacialis CV from the Fram Strait (Figure 3), mean clearance
rates were 1.4– 4.7 ml copepod21 h21, and ingestion rates varied
from 0.006 to 0.013 mg chl a copepod21 h21 independent from
CO2 conditions (Table 3). There was no correlation between IR
and the initial chl a concentration, while for copepods incubated
932
N. Hildebrandt et al.
Table 4. Carbon and nitrogen contents of C. finmarchicus CV
sampled from control and high CO2 mesocosms.
Control CO2
Day
0
8
15
22
28
C (mg)
151 + 34
167 + 26
167 + 26
162 + 12
164 + 25
High CO2
N (mg)
19 + 2
19 + 2
19 + 2
19 + 1
18 + 2
n
19
11
12
12
12
C (mg)
151 + 34
134 + 17
123 + 23
158 + 12
169 + 26
n
19
8
12
12
12
N (mg)
19 + 2
17 + 1
16 + 2
18 + 1
19 + 2
Values are presented as mean + standard deviation. C, carbon content; N,
nitrogen content; n, number of samples. For each sample, 2 –6 copepods
(usually 5) were pooled. In the control CO2 group, all copepods initially
sampled from the control mesocosm are included (i.e. also copepods from the
immediate response group which were transferred to high pCO2 during the
grazing experiments). Likewise, in the high CO2 group, all copepods initially
sampled from the high CO2 mesocosm are represented.
Table 5. Spearman rank-order correlation analyses between carbon
and nitrogen content in C. finmarchicus CV and time during 28 d of
the SOPRAN mesocosm experiment 2011.
[CO2] (matm)
390
3000
390
3000
Parameter
C
C
N
N
Correlation coefficient
0.167
0.256
0.019
0.139
p
0.180
0.043
0.881
0.275
Values presented in bold indicate significant correlations between C and N
content and time.
[CO2], CO2 concentration; C, carbon content; N, nitrogen content.
at 390 and 1120 matm CO2, a negative correlation between CR and
chl a was found (p ¼ 0.009). This indicates that food uptake was not
limited during the grazing experiments but copepods at 390 and
1120 matm CO2 had to filter more water to ingest the same
amount of algae compared with copepods from 3000 matm.
The C and N contents of C. glacialis (3.5 + 0.1 mm prosome
length) at the start of the incubation were 646 and 56 mg, respectively (Table 6). Over time, the N content increased significantly
by 30 –40% at all CO2 concentrations. Also the carbon content
increased, however, significantly only in copepods kept at 1120 and
3000 matm CO2 (Table 7). The pCO2 did not have significant effects
on body mass, with two exceptions. On Day 15, the C content in copepods from 390 matm was significantly lower when compared with the
other CO2 treatments (Holm-Sidak test, p ≤ 0.004), whereas on Day
16 copepods from 1120 matm had significantly more body carbon
than those from 3000 matm CO2 (p ¼ 0.011).
Discussion
Ocean acidification (OA) has been shown to influence feeding rates
of marine organisms. In the common sea star Asterias rubens, for
example, which does not compensate for elevated extracellular pCO2
under environmental hypercapnia, feeding rates are lower when
exposed to OA than under normocapnic conditions (Appelhans
et al., 2012). Also in larval sea urchins, i.e. Strongylocentrotus droebachiensis and Dendraster excentricus, and in larvae of the gastropod
Concholepas concholepas, food uptake was significantly impaired
by elevated seawater pCO2 (Dupont and Thorndyke, 2008; Chan
et al., 2011; Vargas et al., 2013). Other species regulate the extracellular pH, such as the shore crab Carcinus maenas. Feeding in this
species was reduced at high when compared with low pCO2
Figure 3. Response of C. glacialis CV to OA: clearance rate (a) and
ingestion rate (b) at control (white circles), intermediate (grey circles),
and high pCO2 (black circles). Data are presented as mean + standard
deviation.
during a 10-week incubation experiment, but not in short-term
feeding assays (Appelhans et al., 2012). The authors suggested that
during long-term exposure additional energy had to be allocated
to acid–base regulation, which affected energy demanding processes related to feeding such as digestion or prey handling
(Appelhans et al., 2012). In contrast, the Antarctic krill Euphausia
superba ingested more food at elevated pCO2 (Saba et al., 2012),
and this study discussed that the increase in feeding compensated
for elevated energetic needs due to acid–base regulation. Li and
Gao (2012) came to a similar conclusion in their study on the
copepod Centropages tenuiremis, although the differences in
grazing rates were not significant. In Pseudocalanus acuspes from
the Svalbard area, elevated CO2 concentrations led to increased ingestion rates at intermediate and high food concentrations;
however, respiration rates were not significantly affected by pCO2
(Thor and Oliva, 2015).
Calanus glacialis was incubated at relatively stable CO2 concentrations throughout our experiments, simulating a realistic scenario
that is projected to occur in about the year 2100 (1120 matm) and an
extreme scenario (3000 matm) that is not realistic for surface waters
(Caldeira and Wickett, 2003). Calanus finmarchicus were sampled
from large-scale mesocosms which were initially adjusted to 390
and 3000 matm CO2. In the high CO2 mesocosm, the pH increased
by 0.2 –0.6 units over time, depending on the water depth, and thus,
C. finmarchicus in this mesocosm was not kept at a stable pCO2.
933
Ocean acidification does not alter grazing in Calanus spp.
Table 6. Prosome length, carbon, and nitrogen contents of C. glacialis CV incubated at different CO2 concentrations.
390 matm CO2
Day
0
1
4
8
12
15
16
C (mg)
646 + 168
789 + 124
704 + 137
713 + 74
719 + 93
693 + 159
725 + 85
1120 matm CO2
N (mg)
56 + 12
69 + 9
64 + 9
70 + 5
72 + 9
71 + 18
73 + 7
n
36
9
6
8
9
44
9
C (mg)
646 + 168
674 + 105
743 + 134
736 + 63
747 + 60
788 + 140
778 + 58
3000 matm CO2
N (mg)
56 + 12
63 + 7
71 + 11
71 + 6
66 + 22
77 + 17
78 + 7
n
36
9
6
6
9
41
9
C (mg)
646 + 168
687 + 55
629 + 94
702 + 108
672 + 104
783 + 132
685 + 67
N (mg)
56 + 12
63 + 4
61 + 8
62 + 22
65 + 8
76 + 16
72 + 8
n
36
10
9
9
8
43
9
Values are presented as mean + standard deviation.
C, carbon content; N, nitrogen content; N, number of samples; usually 3 –4 copepods were pooled for analyses (n highlighted in bold); single copepods
measurements are indicated by regular numbers.
Table 7. Spearman rank-order correlation analyses between carbon
and nitrogen content in C. glacialis CV and time during 16 d of
incubation on-board RV Polarstern in 2012.
[CO2] (matm)
390
1120
3000
390
1120
3000
Parameter
C
C
C
N
N
N
Correlation coefficient
0.117
0.391
0.299
0.471
0.625
0.596
p
0.200
<0.001
<0.001
<0.001
<0.001
<0.001
[CO2], CO2 concentration; C, carbon content; N, nitrogen content. Values
presented in bold indicate significant correlations between C and N content
and time.
There were, however, marked differences in pH between control and
high CO2 mesocosms throughout the study, which allowed for
detecting possible changes in feeding activity due to OA.
Ingestion rates are generally sigmoidally related to the food concentration (e.g. Kiørboe et al., 1982; Urban-Rich et al., 2004). Thus,
a compensation for elevated energy demands via increased feeding
rates is likely only detected under non-limiting food concentrations,
as was the case during our study. The final chl a content in the
incubation bottles at the end of the grazing experiments with
C. finmarchicus ranged between 5.6 and 9.5 mg l21 (Table 2),
which is higher than typically found during spring phytoplankton
blooms in western Norwegian coastal areas and the Norwegian
Sea (Meyer-Harms et al., 1999; Larsen et al., 2004; Husa et al.,
2014) and also above the peak of the artificially induced phytoplankton bloom in the mesocosms which ranged between 3 and 5 mg l21
chl a. During the shipboard experiments with C. glacialis, final chl a
concentrations were between 1.4 and 4.3 mg l21 (Table 2), which is
similar to bloom conditions in Arctic waters (Wu et al., 2007;
Cherkasheva et al., 2014). Furthermore, in both species, IR were
not significantly correlated with the chl a content, while correlations
between CR and chl a were either negative or not significant. This
also indicates that algae were provided in excess and the copepods
were not food limited throughout the grazing experiments. In the
6 l CO2 incubation bottles on-board RV Polarstern, we did not
monitor chl a. However, we provided algal concentrations which
were 4 times higher than during the incubation for measuring
grazing rates while the copepod densities were at maximum only
2.5 times higher when compared with the grazing experiments.
In addition, C and N contents of C. glacialis increased and we therefore believe that the copepods were not food limited during the
long-term incubation.
High food concentrations, on the other hand, might bear the
risk that grazing rates of the copepods are already at or close to
the maximum physiological feeding capacity. This would hinder
the copepods to increase their feeding rates as a response to OA
stress. However, Urban-Rich et al. (2004) found ingestion rates
of up to 0.04 mg chl a copepod21 h21 for C. finmarchicus CIV
and CV while the rates during our experiment did not exceed
0.027 mg chl a copepod21 h21. Also for C. glacialis, higher CR and
IR than measured in our study were reported (Tande and Båmstedt,
1985). We thus believe that, despite high food supply, the copepods
would have been able to increase their grazing rates if environmental
hypercapnia had led to additional energy demands.
Our data, however, indicate that elevated seawater pCO2 did not
affect the grazing activity of C. finmarchicus and C. glacialis, neither
after sudden changes in pCO2 nor after 2 –4 weeks of exposure. We
found significant differences in grazing between copepods from
control and high pCO2 treatments only on one occasion and there
was no consistent trend, neither to higher nor lower grazing activity
under OA scenarios. All copepods from control and high pCO2
treatments were fed with diatoms, i.e. Thalassiosira weissflogii,
which were grown at control conditions. The copepods thus
received food organisms of the same quality. De Kluijver et al.
(2013) inferred from a calculation of the amount of incorporated
13
C during a mesocosm study in an Arctic fjord that the food
uptake of Calanus spp. decreased at elevated CO2 concentrations.
Their approach, however, addressed both direct and indirect
effects of OA, as CO2 affected the algal community composition
in the mesocosms (Brussaard et al., 2013; Leu et al., 2013; Schulz
et al., 2013) and therefore the food quality for the copepods.
When ingestion rates are similar, differences in body weight may
serve as another indicator for changes in energy demands due to elevated pCO2, i.e. the copepod body mass may increase to a lesser
extent or even decrease if coping with OA stress is energetically
costly. In our laboratory experiments, however, the body mass of
C. glacialis kept at low, medium, and high CO2 levels was not significantly different and, thus, there was no indication for additional
energy demands. Only during the mesocosm experiments, we
found significantly lower body mass in C. finmarchicus CV from the
high pCO2 mesocosm on 2 d (Days 8 and 15). This may be attributed
to lower food quality in high pCO2 mesocosms as the phytoplankton community changed with pCO2 (J. R. Bermúdez Monsalve
(GEOMAR), pers. comm.). At day 14, nutrients were added, which
induced a phytoplankton bloom (KGS and UR, unpublished data).
The food availability thus improved in all mesocosms and this could
explain why there were no differences in body mass at later sampling
dates.
934
In conclusion, we did not find direct effects of elevated pCO2 on
the copepods grazing rates and body mass, neither in C. finmarchicus
nor in C. glacialis, suggesting that the energy demand of these two
Calanus species does not increase when exposed to future OA.
The mechanisms responsible for the tolerance to OA in C. finmarchicus and C. glacialis, as was also reported in other studies
(Mayor et al., 2007; Weydmann et al., 2012; Niehoff et al., 2013;
Hildebrandt et al., 2014), remain unknown. Just recently, a seasonal
study on C. glacialis has shown that this species strongly regulates its
extracellular acid–base status, exhibiting extracellular pH (pHe)
values as low as 5.5 during winter (i.e. during diapause) and high
pHe (7.9) during summer (Freese et al., 2015). Similar mechanisms
were also reported from two diapausing Antarctic copepod species
(Sartoris et al., 2010; Schründer et al., 2013). Compensating for
comparably small shifts in seawater pH due to environmental hypercapnia might therefore not be a challenge for these copepods.
Acknowledgements
We thank J. Büdenbender, D. Freese, and all scientists on site for
their help in copepod sampling and sorting during the SOPRAN
mesocosm study. Furthermore, we acknowledge the support of
S. Koch Klavsen and A. Ludwig in chlorophyll a measurements
during the mesocosm study and of M. Bullwinkel who measured
DIC. N. Knüppel and the officers and crew of RV Polarstern are
thanked for their help in copepod sampling in Fram Strait. E.
Allhusen kindly provided algae cultures. Two anonymous reviewers
are thanked for their valuable comments which have improved our
manuscript.
Funding
Financial support was provided by the Federal Ministry of
Education and Research (BMBF) through the projects SOPRAN
(FKZ 03F0611A) and BIOACID (FKZ 03F0608).
References
Alcamo, J., Bouwman, A., Edmonds, J., Grübler, A., Morita, T., and
Sugandhy, A. 1995. An evaluation of the IPCC IS92 emission scenarios. In Climate Change 1994, pp. 247– 304. Ed. by J. T.
Houghton, L. G. Meira Filho, J. Bruce, H. Lee, B. A. Callander, E.
Haites, N. Harris, et al. Cambridge University Press, Cambridge,
New York, Melbourne. 339 pp.
Appelhans, Y. S., Thomsen, J., Pansch, C., Melzner, F., and Wahl, M.
2012. Sour times: seawater acidification effects on growth, feeding
behaviour and acid-base status of Asterias rubens and Carcinus
maenas. Marine Ecology Progress Series, 459: 85 – 97.
Brussaard, C. P. D., Noordeloos, A. A. M., Witte, H., Collenteur, M. C. J.,
Schulz, K., Ludwig, A., and Riebesell, U. 2013. Arctic microbial community dynamics influenced by elevated CO2 levels. Biogeosciences,
10: 719 –731.
Caldeira, K., and Wickett, M. E. 2003. Anthropogenic carbon and ocean
pH. Nature, 425: 365.
Chan, K. Y. K., Grünbaum, D., and O’Donnell, M. J. 2011. Effects of
ocean-acidification-induced morphological changes on larval
swimming and feeding. The Journal of Experimental Biology, 214:
3857– 3867.
Charalampopoulou, A., Poulton, A. J., Tyrrell, T., and Lucas, M. 2008.
Surface seawater carbonate chemistry, nutrients and phytoplankton
community composition on a transect between North Sea and Arctic
Ocean. doi:10.1594/PANGAEA.763990.
Cherkasheva, A., Bracher, A., Melsheimer, C., Köberle, C., Gerdes, R.,
Nöthig, E.-M., Bauerfeind, E., et al. 2014. Influence of the physical
environment on polar phytoplankton blooms: a case study in the
Fram Strait. Journal of Marine Systems, 132: 196 –207.
N. Hildebrandt et al.
Conover, R. J. 1988. Comparative life histories in the genera Calanus
and Neocalanus in high latitudes of the northern hemisphere.
Hydrobiologia, 167/168: 127 –142.
Cripps, G., Lindeque, P., and Flynn, K. J. 2014. Have we been underestimating the effects of ocean acidification in zooplankton? Global
Change Biology, 20: 3377– 3385.
De Kluijver, A., Soetaert, K., Czerny, J., Schulz, K. G., Boxhammer, T.,
Riebesell, U., and Middelburg, J. J. 2013. A 13C labeling study on
carbon fluxes in Arctic plankton communities under elevated CO2
levels. Biogeosciences, 10: 1425– 1440.
Dupont, S., and Thorndyke, M. C. 2008. Ocean acidification and its
impact on the early life-history stages of marine animals. CIESM
Workshop Monographs, 36: 89 – 97.
Falk-Petersen, S., Pavlov, V., Timofeev, S., and Sargent, J. R. 2007.
Climate variability and possible effects on arctic food chains: The
role of Calanus. In Arctic Alpine Ecosystems and People in a
Changing Environment, pp. 147– 166. Ed. by J. B. Ørbæk, R.
Kallenborn, I. Tombre, E. N. Hegseth, S. Falk-Petersen, and A. H.
Hoel. Springer, Berlin, Heidelberg. 434 pp.
Freese, D., Niehoff, B., Søreide, J. E., and Sartoris, F. J. 2015. Seasonal
patterns in extracellular ion concentrations and pH of the Arctic
copepod Calanus glacialis. Limnology and Oceanography, 60:
2121– 2129.
Friedlingstein, P., Houghton, R. A., Marland, G., Hackler, J., Boden, T.
A., Conway, T. J., Canadell, J. G., et al. 2010. Update on CO2 emissions. Nature Geoscience, 3: 811 –812.
Frost, B. W. 1972. Effects of size and concentration of food particles on
the feeding behavior of the marine planktonic copepod Calanus
pacificus. Limnology and Oceanography, 17: 805 – 815.
Guillard, R. R. L. 1975. Culture of phytoplankton for feeding marine
invertebrates. In Culture of Marine Invertebrate Animals, pp.
26 – 60. Ed. by W. L. Smith, and M. H. Chanley. Plenum Press,
New York. 338 pp.
Hildebrandt, N., Niehoff, B., and Sartoris, F. J. 2014. Long-term effects
of elevated CO2 and temperature on the Arctic calanoid copepods
Calanus glacialis and C. hyperboreus. Marine Pollution Bulletin,
80: 59 – 70.
Hirche, H.-J. 1998. Dormancy in three Calanus species (C. finmarchicus,
C. glacialis and C. hyperboreus) from the North Atlantic. Archiv fur
Hydrobiologie Special Issues Advances in Limnology, 52: 359 – 369.
Husa, V., Kutti, T., Ervik, A., Sjøtun, K., Hansen, P. K., and Aure, J. 2014.
Regional impact from fin-fish farming in an intensive production
area (Hardangerfjord, Norway). Marine Biology Research, 10:
241– 252.
Isari, S., Zervoudaki, S., Saiz, E., Pelejero, C., and Peters, J. 2015.
Copepod vital rates under CO2-induced acidification: a calanoid
species and a cyclopoid species under short-term exposures.
Journal of Plankton Research, 37: 912– 922.
Jaschnov, W. A. 1970. Distribution of Calanus species in the seas of the
northern hemisphere. Internationale Revue der Gesamten
Hydrobiologie und Hydrographie, 55: 197 – 212.
Jutterström, S., Anderson, L. G., Bates, N. R., Bellerby, R., Johannessen,
T., Jones, E. P., Key, R. M., et al. 2010. Arctic Ocean data in CARINA.
Earth System Science Data, 2: 71 – 78.
Kiørboe, T., Møhlenberg, F., and Nicolajsen, H. 1982. Ingestion rate and
gut clearance in the planktonic copepod Centropages hamatus
(Lilljeborg) in relation to food concentration and temperature.
Ophelia, 21: 181 – 194.
Kurihara, H., Shimode, S., and Shirayama, Y. 2004. Effects of raised CO2
concentration on the egg production rate and early development of
two marine copepods (Acartia steueri and Acartia erythraea). Marine
Pollution Bulletin, 49: 721– 727.
Larsen, A., Fonnes Flaten, G. A., Sandaa, R.-A., Castberg, T., Thyrhaug,
R., Erga, S. R., Jacquet, S., et al. 2004. Spring phytoplankton bloom
dynamics in Norwegian coastal waters: microbial community succession and diversity. Limnology and Oceanography, 49: 180 –190.
Ocean acidification does not alter grazing in Calanus spp.
Lee, R. F. 1974. Lipid composition of the copepod Calanus hyperboreas
from the Arctic ocean. Changes with depth and season. Marine
Biology, 26: 313 – 318.
Leu, E., Daase, M., Schulz, K. G., Stuhr, A., and Riebesell, U. 2013. Effect
of ocean acidification on the fatty acid composition of a natural
plankton community. Biogeosciences, 10: 1143– 1153.
Lewis, E., and Wallace, D. W. R. 1998. CO2SYS – program developed for
the CO2 system calculations. Report ORNL/CDIAC-105. Carbon
Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, TN, USA. 21 pp.
Li, W., and Gao, K. 2012. A marine secondary producer respires and
feeds more in a high CO2 ocean. Marine Pollution Bulletin, 64:
699– 703.
Longhurst, A. R. 1985. The structure and evolution of plankton communities. Progress in Oceanography, 15: 1 – 35.
Marshall, S. M., and Orr, A. P. 1955. On the biology of Calanus finmarchicus VIII. Food uptake, assimilation and excretion in adult and stage
V Calanus. Journal of the Marine Biological Association of the
United Kingdom, 34: 495 – 529.
Mayor, D. J., Everett, N. R., and Cook, K. B. 2012. End of century ocean
warming and acidification effects on reproductive success in a temperate marine copepod. Journal of Plankton Research, 34: 258 – 262.
Mayor, D. J., Matthews, C., Cook, K., Zuur, A. F., and Hay, S. 2007.
CO2-induced acidification affects hatching success in Calanus finmarchicus. Marine Ecology Progress Series, 350: 91 – 97.
McConville, K., Halsband, C., Fileman, E. S., Somerfield, P. J., and
Findlay, H. S. 2013. Effects of elevated CO2 on the reproduction of
two calanoid copepods. Marine Pollution Bulletin, 73: 428– 434.
Melzner, F., Stange, P., Trübenbach, K., Thomsen, J., Casties, I.,
Panknin, U., Gorb, S. N., et al. 2011. Food supply and seawater
pCO2 impact calcification and internal shell dissolution in the blue
mussel Mytilus edulis. PLoS ONE, 6: e24223.
Meyer-Harms, B., Irigoien, X., Head, R., and Harris, R. 1999. Selective
feeding on natural phytoplankton by C. finmarchicus before,
during, and after the 1997 spring bloom in the Norwegian Sea.
Limnology and Oceanography, 44: 154– 165.
Michaelidis, B., Ouzounis, C., Paleras, A., and Pörtner, H. O. 2005.
Effects of long-term moderate hypercapnia on acid-base balance
and growth rate in marine mussels Mytilus galloprovincialis.
Marine Ecology Progress Series, 293: 109– 118.
Miles, H., Widdicombe, S., Spicer, J. I., and Hall-Spencer, J. 2007. Effects
of anthropogenic seawater acidification on acid-base balance in the
sea urchin Psammechinus miliaris. Marine Pollution Bulletin, 54:
89 – 96.
Niehoff, B., Schmithüsen, T., Knüppel, N., Daase, M., Czerny, J., and
Boxhammer, T. 2013. Mesozooplankton community development
at elevated CO2 concentrations: results from a mesocosm experiment in an Arctic fjord. Biogeosciences, 10: 1391– 1406.
Pasternak, A., Arashkevich, E., Tande, K., and Falkenhaug, T. 2001.
Seasonal changes in feeding, gonad development and lipid stores
in Calanus finmarchicus and C. hyperboreus from Malangen, northern Norway. Marine Biology, 138: 1141 –1152.
Pedersen, S. A., Hansen, B. H., Altin, D., and Olsen, A. J. 2013.
Medium-term exposure of the North Atlantic copepod Calanus finmarchicus (Gunnerus, 1770) to CO2-acidified seawater: effects on
survival and development. Biogeosciences, 10: 7481– 7491.
Pörtner, H. O., Reipschläger, A., and Heisler, N. 1998. Acid-base regulation, metabolism and energetics in Sipunculus nudus as a function
of ambient carbon dioxide level. Journal of Experimental Biology,
201: 43 –55.
Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P.,
Riebesell, U., Shepherd, J., et al. 2005. Ocean acidification due to increasing atmospheric carbon dioxide. Policy document 12/05, The
Royal Society, London, UK. 60 pp.
Reipschläger, A., and Pörtner, H. O. 1996. Metabolic depression during
environmental stress: the role of extracellular versus intracellular pH
935
in Sipunculus nudus. The Journal of Experimental Biology, 199:
1801– 1807.
Riebesell, U., Czerny, J., von Bröckel, K., Boxhammer, T., Büdenbender,
J., Deckelnick, M., Fischer, M., et al. 2013. Technical note: a mobile
sea-going mesocosm system – new opportunities for ocean change
research. Biogeosciences, 10: 1835– 1847.
Rosa, R., and Seibel, B. A. 2008. Synergistic effects of climate-related
variables suggest future physiological impairment in a top oceanic
predator. Proceedings of the National Academy of Sciences of the
United States of America, 105: 20776– 20780.
Saba, G. K., Schofield, O., Torres, J. J., Ombres, E. H., and Steinberg, D.
K. 2012. Increased feeding and nutrient excretion of adult Antarctic
krill, Euphausia superba, exposed to enhanced carbon dioxide
(CO2). PLoS ONE, 7: e52224.
Sartoris, F. J., Thomas, D. N., Cornils, A., and Schnack-Schiel, S. B. 2010.
Buoyancy and diapause in Antarctic copepods: the role of ammonium accumulation. Limnology and Oceanography, 55: 1860– 1864.
Schründer, S., Schnack-Schiel, S. B., Auel, H., and Sartoris, F. J. 2013.
Control of diapause by acidic pH and ammonium accumulation
in the hemolymph of Antarctic copepods. PLoS ONE, 8: e77498.
Schulz, K. G., Bellerby, R. G. J., Brussaard, C. P. D., Büdenbender, J.,
Czerny, J., Engel, A., Fischer, M., et al. 2013. Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels
of atmospheric carbon dioxide. Biogeosciences, 10: 161– 180.
Seibel, B. A., Maas, A. E., and Dierssen, H. M. 2012. Energetic plasticity
underlies a variable response to ocean acidification in the pteropod,
Limacina helicina antarctica. PLoS ONE, 7: e30464.
Solomon, S., Quin, D., Manning, M., Alley, R. B., Berntsen, T., Bindoff,
N. L., Chen, Z., et al. 2007. Technical summary. In Climate Change
2007: The Physical Science Basis. Contribution of Working Group I
to the Fourth Assessment Report of the Intergovernmental Panel on
Climate Change, pp. 20– 91. Ed. by S. Solomon, D. Quin, M.
Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, et al.
Cambridge University Press, Cambridge and New York. 996 pp.
Tande, K. S., and Båmstedt, U. 1985. Grazing rates of the copepods
Calanus glacialis and C. finmarchicus in arctic waters of the Barents
Sea. Marine Biology, 87: 251– 258.
Tande, K. S., Hassel, A., and Slagstad, D. 1985. Gonad maturation and
possible life cycle strategies in Calanus finmarchicus and Calanus glacialis in the northwestern part of the Barents Sea. In Marine Biology
of the Polar Regions and Effects of Stress on Marine Organisms, pp.
141– 155. Ed. by J. S. Gray, and M. E. Christiansen. John Wiley &
Sons Ltd, New York. 660 pp.
Tans, P. 2014. Trends in Atmospheric Carbon Dioxide. NOAA/ESRL,
Boulder, CO, USA. http://www.esrl.noaa.gov/gmd/ccgg/trends/
(last accessed 23 November 2015).
Thomsen, J., and Melzner, F. 2010. Moderate seawater acidification does
not elicit long-term metabolic depression in the blue mussel Mytilus
edulis. Marine Biology, 157: 2667– 2676.
Thor, P., and Dupont, S. 2015. Transgenerational effects alleviate severe
fecundity loss during ocean acidification in a ubiquitous planktonic
copepod. Global Change Biology, 21: 2261– 2271.
Thor, P., and Oliva, E. O. 2015. Ocean acidification elicits different energetic responses in an Arctic and a boreal population of the copepod
Pseudocalanus acuspes. Marine Biology, 162: 799– 807.
Urban-Rich, J., McCarty, J. T., and Shailer, M. 2004. Effects of food
concentration and diet on chromophoric dissolved organic matter
accumulation and fluorescent composition during grazing experiments with the copepod C. finmarchicus. ICES Journal of Marine
Sciences, 61: 542– 551.
Vargas, C. A., de la Hoz, M., Aguilera, V., San Martin, V., Manrı́quez,
P. H., Navarro, J. M., Torres, R., et al. 2013. CO2-driven ocean acidification reduces larval feeding efficiency and change food selectivity in the mollusc Concholepas concholepas. Journal of Plankton
Research, 35: 1059– 1068.
Weydmann, A., Søreide, J. E., Kwasniewski, S., and Widdicombe, S.
2012. Influence of CO2-induced acidification on the reproduction
936
of a key Arctic copepod Calanus glacialis. Journal of Experimental
Marine Biology and Ecology, 428: 39– 42.
Widdicombe, S., and Spicer, J. I. 2008. Predicting the impact of ocean
acidification on benthic biodiversity: What can animal physiology
tell us? Journal of Experimental Marine Biology and Ecology, 366:
187– 197.
Wood, H. L., Spicer, J. I., and Widdicombe, S. 2008. Ocean acidification
may increase calcification rates, but at a cost. Proceedings of the
Royal Society B, 275: 1767– 1773.
N. Hildebrandt et al.
Wu, Y., Peterson, I. K., Tang, C. C. L., Platt, T., Sathyendranath, S., and
Fuentes-Yaco, C. 2007. The impact of the sea ice on the initiation of
the spring bloom in the Newfoundland and Labrador Shelves.
Journal of Plankton Research, 29: 509– 514.
Zhang, D., Li, S., Wang, G., and Guo, D. 2011. Impacts of CO2-driven
seawater acidification on survival, egg production rate and hatching
success of four marine copepods. Acta Oceanologica Sinica, 30:
86 – 94.
Handling editor: Stéphane Plourde